1. Field of the Invention
This invention relates to conducting tubes for the transport of intensely cold media, and more particularly to a conducting tube comprising two corrugated metal tubes arranged concentrically with a superinsulation layer therebetween.
2. Description of the Prior Art
The term `intensely cold media` in the sense of the invention refers to media with a temperature below 100 degrees K, e.g., liquefied gases such as helium, oxygen, nitrogen, etc.
For the transport of media of this type, a conducting tube is known from U.S. Pat. No. 3,240,234. In this conducting tube, a helically wound superinsulation layer serves as a spacer for the concentric tubes. The superinsulating layer comprises alternately superposed layers of insulating material and reflection material. This design involves a number of disadvantages. For example, in the case of a horizontal installation, the inner tube will be supported on the superinsulation with its own weight and the weight of the medium flowing in the inner tube. Since the superinsulation layer, in order to achieve the maximum possible insulating effect, must be loosely wound, the superinsulation layer below the inner tube will be compressed and will lose its optimal insulating action in that area. As a result of the compression, the inner tube will be displaced in its position with respect to the outer tube, so that an increased incidence of heat occurs in the area of the compressed superinsulation layer due to both the smaller separation and the lost insulation value. A further significant disadvantage is the fact that, particularly in the case of large lengths of the conducting tube, an evacuation of the superinsulation layer is not possible or is possible only with a large expenditure of time.
In another embodiment of a conducting tube shown in U.S. Pat. No. 3,595,275, a helically proceeding spacer is located on the inner tube. The superinsulation layer is wound over this spacer and is in contact with the inner tube in the regions located between two adjacent helices. Between the outer surface of the spacer and the inner surface of the outer tube, the superinsulation layer is very strongly compressed, so that an increased incidence of heat occurs at these points. With this design also, it is not possible to evacuate large lengths in an economical manner due to the contact between the superinsulation layer and the inner tube. In addition, this conducting tube is burdened by the disadvantage that the spacer helix consists of a strip of the superinsulation layer, whose individual layers will have to be bonded to each other in a separate working stage, e.g., by wrapping a thread around them, wrapping them in a foil, or by quilting. As a result, this design of the conducting tube becomes very expensive. During winding of the multi-layer spacer, problems appear, since the outer layers stretch while the inner layers are compressed.